Please and Thankyou

Please and thankyou seem to be one of the most repeated phrases that a child will hear from their parents.
In order to teach manners to a child, a parent responds to child that has asked for a drink of water of something of that kind, with "please". This is said to encourage the child to use manners.
While there is nothing wrong with this theory of teaching manners to children, consider this for just a moment.
Kids have a habit of copying everything they hear, especially from their parents, as a child sees and hears more from them than any other person. Now think about how often an adult says please or thankyou. I have watched so many parents ask their children to politely do something, but many times, the request was asked without a please, and when it was done, no thankyou either (most of the time of course there was a please and a thankyou).
Considering a child copies nearly everything parents do, a child not hearing a please and thankyou all the time, will of course copy what they have heard, this is nothing like how an adult would think, in the sense of "they didn't say it so why should I", this is just purely and simply copying.
How can we avoid this from happening, well one thing I did, was to stop asking my daughter for a please or a thankyou for nearly everything, with just the occasional mention of it.
The reason why I thought of trying this was quite simple. It was obvious to me that when she had learnt a word such as cat, more, again or car, she had retained those words for ever, so I figured that if she had learnt those words and said them without prompting, then please and thankyou are no different.
Turns out that the theory has worked and she now (at the age of 2 years 1 month) says please and thankyou, not all the time though, but she does say it without any prompting.
Another way to get a child to use these words would to be mindful of how often you use the words yourself, if possible use them every single time.
Or possibly, don't expect a please or thankyou from your child with every request that they make, if they do use please or thankyou without prompting, make the biggest deal about it possible, just to show how well the child has done. You will find that the encouragement will improve the use of these words.